This invention relates to abrasive articles having oriented abrasive particles in a matrix and to a method of making such abrasive articles.
There are many prior methods disclosed for incorporating and positioning certain types of abrasive particles in a sheet-like matrix. Such abrasive particles include diamond crystals and crystalline cubic boron nitride (CBN). Each of these abrasive materials is known to provide optimal abrasive performance when the abrasive particles are optimally positioned in the matrix which holds them in the abrasive product. Various attempts have been made to optimally position such abrasive particles in such abrasive products, but they have met with only limited success in the optimal orientation of abrasive particles. The following references provide some indication of what has been done in the past to provide a solution to this problem.
U.S. Pat. No. 4,680,199 (Vontell); U.S. Pat. Nos. 4,925,457 and 5,092,910 (de Kok); U.S. Pat. No. 5,525,100 (Kelly); U.S. Pat. No. 5,725,421 (Goers); U.S. Pat. No. 5,551,960 (Christianson); U.S. Pat. No. 5,049,165 (Tselesin); U.S. Pat. No. 5,380,390 (Tselesin); U.S. Pat. No. 5,620,489 (Tselesin); U.S. Pat. No. 6,110,031 (Preston); U.S. Pat. No. 5,791,330 (Tselesin); U.S. Pat. No. 5,695,533 (Kardys); U.S. Pat. No. 5,817,204 (Tselesin); U.S. Pat. No. 5,980,678 (Tselesin); N. Tselesin, Improvements of Diamond Tools for Machining of Advanced Engineered Ceramics in xe2x80x9cUsing Advanced Ceramics in Manufacturing Applications,xe2x80x9d Conference Paper, Jun. 3-5, 1991, Cincinnati, Ohio, Publication of Society of Manufacturing Engineers, p. EM91-248-3; U.S. Pat. No. 5,190,568 (Tselesin); U.S. Pat. No. 5,203,880 (Tselesin); and U.S. Pat. Nos. 5,560,745 and 5,453,106 (Roberts).
The present invention resides in the discovery of a deficiency in what the art has taught in regards to making abrasive products having optimally oriented shaped abrasive particles. The present invention produces an abrasive product with optimally oriented shaped abrasive particles to provide optimal orientation and alignment of the sharp points of the abrasive particles for effective abrading irrespective of crystallographic orientation.
For the purpose of this invention xe2x80x9coptimal orientationxe2x80x9d refers to the preferred orientation desired by the manufacturer or user of the abrasive product. Optimal orientation may not always include completely erect abrasive particles should some other orientation be desired. The present invention provides a method in which substrates containing tapered or otherwise shaped surface perforated depressions (e.g., square pyramidal or conical) are used to capture and orient individual abrasive particles thereby increasing the probability of a sharp edge or point being deployed in contact with the surface of a workpiece. The shape of the depression is such that it inherently deploys the abrasive particle in an optimal orientation. The substrate within each shaped depression has a perforation which further facilitates the deployment of the abrasive particle contained therein which may permit reducing the pressure on the back side of the substrate. This technique allows the abrasive particles to arrange themselves with points or edges in a desired configuration, e.g., pointing up.
In one aspect the invention provides a method of making an abrasive article comprised of a sheet-like matrix having deployed therein a multiplicity of optimally oriented shaped abrasive particles, each abrasive particle having a shaped base end and an opposite shaped abrading end comprising:
providing a substrate forming apparatus including a first tool having a contact surface including a multiplicity of projections and a second tool having a mating surface, the contact and mating surfaces of said tools, when mated, being capable of deforming said substrate to provide perforated depressions in the substrate capable of receiving in each depression one base end of said abrasive particle and optimally orienting the abrasive particle therein;
providing an embossable, perforatable, sheet-like substrate;
contacting the sheet-like substrate with the contact and mating surfaces of said first and second tools to provide an embossed, perforated, sheet having back surface and an opposite top surface characterized by having a multiplicity of depressions wherein each depression is characterized by having a shape capable of receiving the shaped base end of said shaped abrasive particle and optimally orienting the abrasive particle therein and a perforation through the sheet-like substrate within said depression wherein the perforation is of a size which will not permit the passage of said abrasive particle;
distributing abrasive particles within said depressions substantially with one abrasive particle in each depression of the embossed, perforated sheet;
optimally orienting each abrasive particle in the depression containing the abrasive particle;
creating a pressure differential between the top surface and the back surface of said embossed, perforated sheet wherein a lower pressure is applied to the back surface to hold each oriented abrasive particle within its depression while removing at least a major portion of the abrasive particles not within said depressions from the top surface of said embossed, perforated sheet; and
permanently bonding said abrasive particles in said depressions after they are optimally oriented to provide an abrasive product which includes optimally oriented shaped abrasive particles with abrading ends exposed.
In a further aspect wherein the substrate is sinterable, the invention provides a method of making an abrasive article comprised of a sheet-like matrix having deployed therein a multiplicity of optimally oriented shaped abrasive particles, each abrasive particle having a shaped base end and an opposite shaped abrading end. The method comprises:
providing a substrate forming apparatus including a first tool having a contact surface including a multiplicity of projections and a second tool having a mating surface, the contact and mating surfaces of said tools, when mated, being capable of deforming said substrate to provide perforated depressions in the substrate capable of receiving in each depression one base end of the abrasive particle and optimally orienting the abrasive particle therein;
providing an embossable, perforatable, sinterable sheet-like substrate comprised of sinterable particles and organic binder in a layer borne on a metal foil;
contacting the sheet-like substrate with the contact and mating surfaces of said first and second tools to provide an embossed, perforated, sinterable sheet having back surface provided by said metal foil and an opposite top surface characterized by having a multiplicity of depressions wherein each depression is characterized by having a shape capable of receiving the shaped base end of said shaped abrasive particle and optimally orienting the abrasive particle therein and a perforation through the sheet-like substrate within said depression wherein the perforation is of a size which will not permit the passage of said abrasive particle;
distributing abrasive particles within said depressions substantially with one abrasive particle in each depression of the embossed, perforated, sinterable sheet;
optimally orienting each abrasive particle in the depression containing the abrasive particle;
creating a pressure differential between the top surface and the back surface of said embossed, perforated, sinterable sheet wherein a lower pressure is applied to the back surface to hold each oriented abrasive particle within its depression while removing at least a major portion of the abrasive particles not within said depressions from the top surface of said embossed, perforated, sinterable sheet;
temporarily bonding said abrasive particles in said depressions after they are optimally oriented;
heating the abrasive particle bearing embossed, perforated, sinterable sheet at a sintering temperature to provide on cooling an abrasive product which includes a sintered matrix bearing bonded optimally oriented shaped abrasive particles with abrading ends exposed; and
cooling said abrasive product.
The preferred method is where the contact and the mating surfaces of said tools are each borne on a surface of a roller. The mating surface may be of a particular shape to provide the depressions or it may simply be a flexible sheet having a smooth surface such as a sheet of elastomeric material.
The term xe2x80x9csinterable sheetxe2x80x9d refers to a green sheet comprised of a preformed sheet of heat fusible particles which typically melt on heating (e.g., metal particles) in a temporary organic binder. Such sinterable materials for the purpose of the present invention include brazing compositions. The preferred sinterable layer comprises metal particles and an organic binder and/or a brazing composition. Such a brazing composition may be an active metal braze. Suitable brazing compositions are preferably selected from Nixe2x80x94Crxe2x80x94Si, Nixe2x80x94Crxe2x80x94P, Nixe2x80x94Crxe2x80x94B, Nixe2x80x94Crxe2x80x94Sixe2x80x94B, Cuxe2x80x94Sn, Agxe2x80x94Cu and Nixe2x80x94Sixe2x80x94B alloys.
The sinterable layer provides on heating to the sintering temperature a liquidus phase in a volume sufficient to wet the base ends of the abrasive particles during the heating step and on cooling sufficient to bond the base ends of the abrasive particles within the sintered matrix. For this purpose, it is preferred that the volume be at least 20% based on the total volume of metal particles in the sinterable layer.
Preferred means for optimally orienting the abrasive particles include vibrating the abrasive particles and/or the embossed, perforated, sinterable sheet after the abrasive particles are distributed and held in place by reduced pressure to optimize the abrasive particle orientation. Orienting may also be accomplished by applying a gentle air stream to the particles as they are held in place.
Preferred abrasive particles are selected from substantially cuboctahedral diamond crystals, substantially cuboctahedral cubic boron nitride crystals and various ceramic materials such as alumina-based ceramic material, zirconia-based ceramic material, silicon nitride-based ceramic material and sialon-based ceramic material. Other useful abrasive particles include fused alumina, ceramic alumina, silicon carbide and sol gel-derived alumina based ceramics.
The size of the abrasive particles may be any size useful for the particular application. Preferably the average particle size is in a relatively narrow range to facilitate deposition in the depressions. Preferably the abrasive particle is at least slightly elongated with an aspect ratio of at least 1.5.
The preferred means of temporarily bonding the abrasive particles in the depressions is provided by solvent softening the organic binder so that it bonds to the shaped base end of the abrasive particle and then permitting the solvent to evaporate while continuing to create the differential pressure.
In a further aspect wherein the matrix need not be sintered, the invention provides an abrasive article comprising:
a multiplicity of optimally oriented shaped abrasive particles wherein each abrasive particle has an aspect ratio greater than about 1.5, a shaped base end and an opposite shaped abrading end; and
a sheet-like matrix having a top surface which includes depressions wherein substantially each depression contains and binds therein a shaped base end of an abrasive particle while the opposite abrading end of said abrasive particle is exposed and aligned in an optimal orientation.
In a further aspect wherein the matrix is sintered, the invention provides an abrasive article comprising:
a multiplicity of optimally oriented shaped abrasive particles wherein each abrasive particle has a shaped base end and an opposite shaped abrading end;
a sintered sheet-like matrix having a top surface which includes depressions wherein substantially each depression contains and binds therein a shaped base end of an abrasive particle while the opposite abrading end of said abrasive particle is exposed and aligned in an optimal orientation; and
a metal foil sinter bonded to the matrix providing a bottom surface to said abrasive article.
The abrasive articles of the invention are characterized by having fewer abrasive particles per unit area as compared to conventional coated abrasive products yet the abrasive products of the invention perform better than or at least equal to such conventional coated abrasive products. Thus, the cost of making the product of the invention is reduced, compared to the cost of making conventional abrasive products, since it typically uses less abrasive material. Moreover, the abrasive performance of the products of the invention may be tailored because the present method affords the opportunity to design an abrasive product with optimal performance.
The various features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments and the accompanying drawings.